CQE PI Feature – Joseph Formaggio

From Neutrino Hunter to Qubits Whisperer

Featured in QSEC newsletter in winter 2022

Joseph Formaggio, a professor of physics, explores the nature of neutrinos and their deep connection between particle physics, quantum mechanics and cosmology. Neutrinos are a fundamental particle, that is, basic building blocks of the universe. Every second, trillions of these particles pass through your body. Their mass is so tiny, and they interact so weakly with other matter, that it is nearly impossible to detect them, making it very difficult to study their properties.

Formaggio leads multiple research projects to understand neutrino properties and how they fit into our understanding of the universe. He is a leading member of the KATRIN and Project 8 experiments, which use the process of tritium beta decay —originally proposed by Enrico Fermi— to measure the mass of the neutrino directly.

In a recent milestone that will bear on future discoveries in nuclear and particle physics, KATRIN scientists established a new upper limit on the mass of the neutrino subatomic particle: 0.8 eV/c2. Published in Nature Physics (https://www.nature.com/articles/s41567-021-01463-1), the discovery has pushed our understanding of neutrinos’ mass.

“The idea of using radioactive decays to measure neutrino masses is as old as the idea of the neutrino itself,” says Formaggio. “[Enrico] Fermi himself devised the technique back in the 1930s. But only now do we have the capabilities to make use of the technique to extract the neutrino mass with such precision.”

Formaggio’s group develops novel detector technologies and techniques to better understand the properties of neutrinos and other rare and exotic particles. The group developed the technique of cyclotron radiation emission spectroscopy to accurately measure the energy of electrons emitted in beta decay; a technique now used by the Project 8 experiment.

The Formaggio group is also developing new cryogenic bolometers to better understand neutrino interactions at extremely low energies. Such detectors are part of the upcoming Ricochet experiment, which aims to study the process of coherent neutrino scattering using neutrinos created in nuclear reactors. More recently, the group has been exploring the potential role of quantum sensors and quantum readout systems for the purpose of detecting neutrinos and other weakly interacting particles.

One may be curious how a neutrinos hunter took a hard left and landed into the Quantum Computing field. “I guess you could say there are two common themes in my work: I like to take techniques or methods that are usually seen in one field and I apply it to my field or vice versa. The other is that I often pursue projects where I am explicitly told that there’s no way something will work, and then I make it work.” Formaggio’s approach clearly works; he has produced a successful track record of surprising discoveries across multiple fields.

In 2019 Formaggio was conversing with MIT-CQE Director, MIT Prof. Will Oliver over lunch about the many sources of decoherence that could destabilize a qubit, such as fluctuating magnetic and electric fields, thermal energy, and even interference between qubits. “Everyone is having a problem with getting qubits to last a really long time. The longer they last, the more computations you can do.” Oliver suggested radiation may be a problem. “Your walls have radiation, there’s cosmic rays that cause radiation.” So Formaggio thought, “you’ve come to the right guy.”

So Oliver and Formaggio teamed up to see how they might nail down the effect of low-level environmental radiation on qubits. “Cosmic ray radiation is hard to get rid of,” Formaggio says. “It’s very penetrating, and goes right through everything like a jet stream. If you go underground, that gets less and less. It’s probably not necessary to build quantum computers deep underground, like neutrino experiments, but maybe deep basement facilities could probably get qubits operating at improved levels.”

Many told Formaggio it couldn’t be radiation. But through experimentation the team reported that the low-level, otherwise harmless background radiation that is emitted by trace elements in concrete walls and incoming cosmic rays are enough to cause decoherence in qubits. They found that this effect, if left unmitigated, will limit the performance of qubits to just a few milliseconds.

Given the rate at which scientists have been improving qubits, they may hit this radiation-induced wall in just a few years. To overcome this barrier, scientists will have to find ways to shield qubits — and any practical quantum computers — from low-level radiation, perhaps by building the computers underground or designing qubits that are tolerant to radiation’s effects.

“These decoherence mechanisms are like an onion, and we’ve been peeling back the layers for the past 20 years, but there’s another layer that left unabated is going to limit us in a couple years, which is environmental radiation,” says Oliver. “This is an exciting result, because it motivates us to think of other ways to design qubits to get around this problem.” Formaggio is intrigued by the types of sensitivities these experiments can produce and hopesthere will be more interplay between the two fields.

While the pandemic delayed his plans, Formaggio envisions a sabbatical in France in his future. “I’ll have an opportunity to work on one of my experiments based there while continuing to make Project 8, a longterm experiment, bigger and better.” While he continues to push his detector explorations further, he wants to write and recharge there too.

Formaggio holds a BS degree from Yale University in physics and PhD from Columbia University where he did his dissertation on neutrino physics. Prior to his arrival to MIT in 2005, Formaggio joined the Sudbury Neutrino Observatory as a postdoctoral fellow at the University of Washington, where he was later appointed as a research assistant professor.

Sources and credits: Interview with Prof. Joseph Formaggio and excerpts from MIT News: “On the hunt for neutrinos” by Anne Trafton, “Cosmic Rays may soon stymie quantum computing” by Jennifer Chu, “A new upper limit on the mass of neutrinos” by Laboratory for Nuclear Science, and Formaggio Physics page profile.